The present invention relates to a vertebral osteosynthesis equipment. It also relates to a method for manufacturing an anchor member comprised by this equipment.
To treat the degeneration of one or more vertebral joints, it is well known to use a vertebral osteosynthesis equipment comprising connecting bars intended to connect several vertebrae to be treated to one another and anchor members (pedicle screws and/or laminar hooks) making it possible to connect these bars to the vertebrae. As an example, patent application publication No. WO 98/55038 describes such an equipment.
The bars are curved according to the desired correction of the position of the vertebrae; if necessary, two adjacent anchor members connected to a same bar can be brought closer together or further apart before complete immobilization of the anchor members relative to the bar, to reduce a curvature of the spine in the frontal plane.
At least one anchor member can be of the so-called “tulip” type, i.e., comprising a wider head that forms an engagement duct of the connecting bar, the axis of this duct generally being secant to the axis of this head. This duct is closed, after placement of the connecting bar therein, by a threaded member screwed in the head. The body of the anchor member can be in the form of a threaded rod intended to be screwed in the resected pedicle of a vertebra or in the form of a hook intended to be inserted behind the lamina of a vertebra. The anchor member can be “monoaxial”, i.e., with said head secured to the body, or “polyaxial”, i.e., with said head articulated relative to said body. This articulation is in particular done by arranging a spherical part or sphere portion at the proximal end of said body and arranging, at the base of the head, in the bottom of said housing, a hole for the engagement of the body and a seat for articulated reception of said spherical part or sphere portion.
In practice, the anchor members are placed on the vertebrae, then the connecting bar(s) are curved depending on the repositioning of the vertebrae to be obtained, then these bars are placed in the different engagement ducts formed by the heads of the anchor members, and the threaded members are placed on these heads to retain the bars in said engagement duct; a movement of two adjacent anchor members connected to a same bar can be done at this stage, to bring the two vertebrae closer together or further apart on one side; once this corrections is done, the threaded members are tightened so as to immobilize the bars relative to said heads.
The monoaxial anchor members have the advantage of perfectly transmitting to the vertebrae the corrections imposed by the curvature of the bar(s) and the separating or approach corrections of two vertebrae; they have the major drawback, however, of making it difficult to engage a bar in the duct formed by the heads of the anchor members.
The advantages and drawbacks of the polyaxial anchor members are reversed: the engagement of a bar in the ducts formed by the heads of the anchor members is easy due to the articulation of these heads, but the transmission to the vertebrae of the corrections imposed by the curvature of the bar(s) and the separating or approach corrections of two vertebrae are done imperfectly, for this same reason of articulation of the heads.
It may be considered to use monoaxial anchor members and polyaxial anchor members on a same assembly, which nevertheless has the major drawback of making the placement of the equipment and the performance of corrections of the spinal column much more complex.
Patent application publications Nos. US 2010/036417 A1 and US 2007/093832 A1 describe pieces of equipment not making it possible to resolve the aforementioned drawbacks.